The invention relates to a camshaft assembly for valve-controlled internal combustion engines. The camshaft assembly has two shaft elements which are positioned one inside the other. The elements are supported one inside the other and are rotatable relative to one another to a limited angle or slidable relative to one another for a limited axial distance. In the case of SOHC engines, the elements allow the inlet cams to be adjusted relative to the outlet cams. The second type of adjustment requires axially variable cam contours at a shaft element the invention makes it possible to change the control times of the inlet valve when the engine is in operation, thereby achieving improved torque characteristics, a reduced fuel consumption and improved exhaust gas values. This is of particular interest as far as diesel engines (charged) are concerned. With such a camshaft, cams referred to below as inner cams are connected to the inner shaft and cams referred to below as outer cams are connected to the outer shaft. The outer shaft includes circumferentially distributed wall apertures associated with the fixing parts of the inner cams and the inner cams include axially open slots or recesses which cover a sector of a circle respectively and which are penetrated by axial finger portions of the outer shaft positioned between the wall apertures respectively.
DE 39 43 427 C1, proposes to produce both the inner cams and the outer cams such that they are integral with the inner shaft and outer shaft respectively and subsequently to join the parts or connect them in a force-locking way to the shaft by inserting them or expanding the respective shaft or to weld them thereto after having been inserted. The first case requires complicated components because simple tube or rod portions can no longer be used for the shaft. The second case requires relatively sophisticated technologies to produce a connection capable of bearing torque loads.
DE 39 43 426 C1, proposes camshaft assemblies of the type where the inner cams are secured to the inner shaft by radially plugged-in pins. The outer cams are connected to the outer shaft by force-locking or material-locking means only, with entirely cylindrical pairs of surfaces being connected by being expanded or shrunk or by welding or soldering.
Finally, in DE 40 08 906 C2, inner cams are secured to the inner shaft by means of radially opposed form-fitting means while temporarily subjecting the inner cams to elastic deformation. The outer cams are connected to the outer shaft by applying prior art force-locking methods involving shaft expansion.
The disadvantage of the shafts referred to above is that for producing the force-locking connection by plastically expanding the shaft parts or by shrinking the cams it is necessary to provide vary accurately machined surfaces and accurate fits in order to obtain a connection capable of bearing torque loads. Under very high torque loads, the connections may temporarily loosen, which leads to the cam being rotated on the shaft. This may result in considerable damage to the internal combustion engine. The methods used for producing a material-locking connection, i.e. soldering or welding, are time-consuming and not suitable for mass production purposes.